Instrumentation package and integrated radiation detector

ABSTRACT

An instrumentation package in broad terms includes at least one substantially cylindrical instrumentation component; a substantially cylindrical shield surrounding the instrumentation component, the shield having a diameter less than a standard predetermined diameter; and a sizing sleeve around the shield, thereby increasing the diameter of the sleeve to the standard predetermined diameter. A nuclear detector package is also disclosed that includes a substantially cylindrical crystal element; a photomultiplier tube arranged coaxially with the crystal element; an optical coupler sandwiched between one end of the crystal element and an adjacent end of the photomultiplier tube; the crystal element, optical coupler and photomultiplier tube hermetically sealed within a cylindrical shield; and a flexible support sleeve extending exteriorly along the crystal element and the photomultiplier tube and radially inside the cylindrical shield.

This application is a continuation of application Ser. No. 10/394,656,filed Mar. 24, 2003 now U.S. Pat. No. 7,034,305, which claims benefit ofApplication No. 60/411,788, filed Sep. 19, 2002, and which claimsbenefit of Application No. 60/366,265, filed Mar. 22, 2002.

BACKGROUND OF THE INVENTION

This invention relates to a low cost, high performance instrumentationpackage particularly applicable, but not limited to radiation detectorsused in solid mineral mining or oil well logging operations (referred toin the industry as wireline operations), and to a highly integratedelectro-optical radiation detector for Measurement While Drilling (MWD)or Logging While Drilling (LWD) operations in which the shock andvibration levels are more extreme.

Scintillation packages typically include a scintillation or crystalelement (or simply, crystal) supported within a cylindrical shield. Aconsequence of making scintillation packages sufficiently rugged forreliable use in harsh environments, such as coal mining or oil welllogging, has been some reduction in performance. Making scintillationpackages rugged has also increased the cost of fabrication. Althoughsignificant progress has been made in recent years in the developmentand deployment of scintillation packages which are able to withstandtemperatures of up to about 200° C. and to simultaneously withstandshock and vibration, there remains a need to further improve functionalperformance and reduce cost without compromising reliability whileoperating in harsh environments.

Several factors contribute to reduced performance of scintillationpackages. Thicker glass windows are sometimes used in order to withstandthe thermal and shock loads and to ensure a good hermetic seal. Thickercouplers are sometimes used in order to provide cushioning between thescintillation element and the window and to provide more compliance sothat the scintillation element will be less likely to separate from thecoupler under vibration. These thicker elements in the optical pathresult in loss of light and reduce the field of view of thephotomultiplier that is receiving the light from the package.

Compressive forces around a scintillation element are necessary in orderto minimize movement of the element under vibration and shock since suchmotion will result in unwanted noise being generated in the opticaloutput. Such compressive forces, when applied to some reflectormaterials around the scintillation element cause the material to becomeless reflective and may cause the material to partially “wet” thesurface of the scintillation element. An example of a highly effectivereflector material is a special TEFLON® tape, which is porous. This isone of the most effective reflectors of scintillation-produced light inthe near UV range and it has been widely used for reflectors onscintillation packages for decades. This material is very pliable,however, and if pressed against the surface of a scintillation element,the efficiency of this tape, as a reflector, diminishes. Yet, ascintillation element must be held firmly in order to be used in harshenvironments in order to not break and in order to not producespontaneous scintillations. Various elastomeric materials—pottings,boots, powders and metallic elements—have been used to supportscintillation elements. Each material has its own advantages anddisadvantages and may be chosen accordingly. However, all known methodsof support within scintillation packages using Teflon® tape and certainother reflectors, which have proven to be effective to protect thescintillation element from thermal effects and high temperature, resultin compression of the tape, causing loss in performance. For example, aboot placed around the reflector must be installed in a compressed statein order to prevent movement of the element at ambient temperatures. Atelevated temperatures, the scintillation element expands and increasesthe compressive force. The boot material, typically made from anelastomeric material, also expands to further increase the pressure onthe reflector. Using properly designed metallic supporting elementsimproves this loading problem by limiting maximum pressure on the tape.

In a similar manner, use of porous reflective tape at the rear of thescintillation element may also be affected by the constant pressure ofthe rear spring.

Use of relatively thick stainless steel housings, or shields, around thescintillation element has increased attenuation of gamma radiation as itpasses into the package.

Similarly, several factors contribute to increased cost of ruggedizedscintillation packages. This is particularly true for designs that aredirected toward minimizing the performance weaknesses described above.Replacement of thick glass windows with thinner sapphire windows is morecostly because sapphire is more costly than glass and can besignificantly more costly if processed in only small quantities. Use oftitanium reduces attenuation below that of stainless steel, whilemaintaining high strength, and, for the same strength, can be thinnerthan aluminum. But use of titanium for shields is more costly thanstainless steel. Not only is titanium metal more expensive, titaniumpipe sizes and tubing sizes that are readily available in the industryfor use in manufacturing shields increase the work required to performthe machining of the shields to the required tolerances. Given all thevariables, making special mill runs of extruded titanium pipe in orderto minimize machining costs is not commercially acceptable in mostcases. Therefore, there is a need for a design approach that addressesboth technical and commercial considerations.

Another factor that constrains cost cutting is that there has been adegree of standardization in the industry that places specificrequirements on the external and internal dimensions of many of thecommonly used configurations. These factors and others, when takentogether, result in overall higher costs while providing less thanoptimum functional performance.

Similarly, with regard to complete detector assemblies such as radiationdetectors (typically including a scintillation package coupled by awindow and/or optical coupler to a photomultiplier tube or PMT), used inmining operations (both oil well drilling and solid mineral mining), andin oil well MWD and LWD operations, is that the detector be able tosurvive harsh environments such as high vibration and shock. For much ofthe history of using nuclear radiation (e.g., gamma ray) detectors formining applications, the critical elements inside the detectors as wellas the complete detectors inside a tool housing, have been supportedwith elastomeric materials, sometimes in combination with longitudinallyplaced springs. Such relatively soft elastomeric materials are oftenstill used to provide cushioning or dynamic isolation from shock andvibration. In recent years, the technology has advanced to the use ofmetallic support devices which are effective and use less space.Metallic supports are described in, for example, U.S. Pat. Nos.5,742,057; 5,796,109; 5,962,855; and 6,355,932.

As already mentioned, one element commonly found in a nuclear detector,particularly when a hygroscopic scintillation crystal is used, is awindow arranged between the scintillation crystal and the PMT or otherdevice that converts the scintillations to electrical pulses. Thiswindow is utilized because the hygroscopic crystal must be encased in ahermetically sealed enclosure, and the window allows the scintillationpulses to pass from the enclosure to the PMT. Thick glass windows aretypically used in scintillation packages for use in downholeapplications in order to provide needed strength and in order to providea good hermetic seal.

In an attempt to improve detector performance, configurations have beendevised for eliminating the window by placing the PMT inside ahermetically sealed housing with the crystal. An immediate advantage isthat the light can pass directly from the scintillation crystal, througha thin optical coupler, into the PMT, without having to pass through thewindow and an additional optical coupling. Without the additional twoelements in the light path, less light is lost and the amount of lightfrom each scintillation pulse is brighter, thus increasing the gain ofthe detector. This increased gain, in turn has the particularlyimportant benefit of maintaining the overall gain of the detector abovea minimum level as the gain of the PMT drops due to degradation of itsphotocathode over time at high temperature. The pulse height resolutioncan also be improved by deletion of the crystal window and also thespace that would have been used by the window can then be used to addmore crystal. However, most previous designs that place the PMT andcrystal into a single hermetic housing cannot survive in a harshenvironment, such as in mining operations, and particularly in MWD andLWD operations.

Another attempt to satisfy current needs has been to place both a PMTand crystal inside a hermetically sealed housing, and then todynamically support the PMT and crystal with an elastomeric material.This arrangement is described in U.S. Pat. No. 6,222,192. Due to thewell understood need to prevent bending of the PMT/crystal, anelastomeric cylindrical sleeve is installed around the PMT/Crystal so asto rigidize the PMT/Crystal assembly. This arrangement createsadditional problems, however, and has not proven to be fullysatisfactory for reasons that will be better understood later.

In addition to considerations related to the internal construction of aradiation detector, it is common practice to also use elastomericmaterials externally of the detector, i.e., to support the detector inthe tool cavity or housing into which it must be installed. Again,elastomers take up valuable space and do not provide the high dampingproperties that are desired for dynamic isolation from inducedvibrations. Moreover, the elastomeric support will tend to have a lowresonant frequency that, when combined with the relatively low damping,will produce a relatively high response thus amplifying the vibrationsinduced into the detector. These amplified vibrations increase thechance of producing noise in the detector output, or of even breakingthe crystal or its interface to the PMT. Elastomeric material isincapable of providing support that exhibits the properties of a hardmount during normal or expected vibration levels. Thus, there is a needfor a more effective and space efficient means of supporting theimproved nuclear detector within the tool in which it is to be used.

A need also remains for a reliable, compact, high performance detectorthat can operate for longer periods of time at high temperatures, up to175 Deg. C. or higher while under high vibration and shock conditions.

BRIEF DESCRIPTION OF THE INVENTION

This invention seeks to provide enhanced designs for instrumentationpackages, and especially scintillation detector or neutron detector(e.g., an He3 proportional counter) packages for nuclear radiationdetectors mounted in well logging tools, solid mineral mining or otherharsh environments.

In one exemplary embodiment of a scintillation detector package, aflexible support sleeve (preferably metal) having a polygon shape incross-section is placed around the scintillation or crystal element forsupporting the crystal within a surrounding shield in such a way thatmuch of the reflector material (e.g., reflector tape) wrapped about thecrystal will not be compressed, thus improving performance. Since themetallic sleeve is a more effective dynamic support than an elastomericmaterial, it does not have to be in contact with the entirescintillation surface. The maximum force which occurs at the highesttemperature will be less for a metallic support sleeve than forelastomeric materials. Thus, the support provided by narrow contactstrip portions of the flexible metal sleeve (established by the polygonshape of the sleeve) along the scintillation element is reduced, plusthe areas of the reflective material between these strip portionsremains in an uncompressed state. Also, because the flexible supportsleeve may be shorter in length than the crystal, special, simplesleeves combined with an internal step on the shield may be employed torestrain the flexible support sleeve axially within the shield such thatthe reflector tape will not be compressed in those areas that extendbeyond the support sleeves. In another embodiment, a radial spaceraround the scintillation element, in combination with the flexiblesleeve, optimizes performance of the reflector material.

A flexible metal support sleeve is also inexpensive to manufacture,simple to install reliable, and provides excellent protection fromthermal effects, shock and vibration.

Sapphire windows and thin optical couplers are preferred in that theyimprove transmission of scintillations from the package to the PMT.Sapphire windows are quite strong and can be made hermetic even whenmuch thinner than can be reliably achieved for typical seals betweenglass and stainless steel. Use of a flexible metal sleeve providespredictable, axial restraint of the scintillation element so that theeffects of shock and vibration in the axial direction will not produceexcessive forces on the coupler or the window, and will normally notresult in the crystal bouncing off the coupler, even when the coupler ismade thinner than usual.

A titanium shield can be effectively brazed to a sapphire window.However, the tolerances and configuration of the area where the brazingis performed must be precise to allow a good hermetic seal. Titaniumpipe in standard sizes is expensive and usually requires much machiningto obtain the necessary dimensions. Welded titanium tubing that isappropriately sized for making shields tends to not be round. Ifstandard size tubing is used to produce shields, by the time it ismachined to a round sleeve, the diameter is too small to fit properlyinto tool cavities that are typically standardized to increments of ⅛inch in diameter. A solution is to make shields slightly smaller than isrequired for standard applications, but then to bond a metal wrap to thesurface of the package. Low cost metal tape is a suitable wrap materialhaving acrylic adhesive that is adequate for temperatures up to 150° C.Titanium foil in thickness between 0.001″ and 0.005″ could also bebonded to the shield with readily available high temperature adhesivesor bonding agents. A more effective solution is to install a metallicflexible sleeve around the detector which provides sizing, compliancewith mesh interfaces, compliance with differential therein, expansionand shock isolation. This is particularly applicable in cases wherethere is a need to have the detector supported inside the tool cavity ina hard mounted configuration. The “hard mount” refers to supporting thecrystal with a flexible sleeve such that the friction created by thesleeve prevents it from moving relative to the tool cavity duringexpected levels of vibration. An added advantage of the flexible sleeveis that it will release to provide damped isolation for high shock.

Once the shields are machined to a standard diameter, smaller thantypical, special bands (tooling fixture) may be installed for finalmachining so that the brazing surface can be made round to the requiredprecision, while the shield is being held round by the bands. At thetime of brazing the sapphire window onto a titanium shield, another bandis installed to bring the thin shield, including the surface to bebrazed to the sapphire, back to a round condition. This approacheliminates the need for machining a fine finish onto the outer surfaceof the shield. It also allows use of a precision reamer to finish thebrazing surface. Use of the flexible support sleeve between the shieldand the crystal also eliminates the need for the normally rough-finishedinner surface of the shield to be machined smooth because the flexiblemetal sleeve can be forced into place even with the higher friction ofthe inside of the shield, and/or eliminates the need for an additionalinstallation sleeve.

Another cost factor relates to the quantities produced. Worldwide, thereare possibly less than 10,000 new scintillation packages produced forrugged oil well drilling operations each year. Though these devicesrepresent an enormous economic benefit, when the many requiredconfigurations are considered, the number required of any given size istoo small to allow production on a large scale. In those instances wherestainless steel shields may be precision fitted to achieve a hardmounted configuration, the hard mounted result can be achieved by usinga flexible sleeve such that the stainless steel shield can be made a“standard size” with much looser tolerances that are less expensive tomanufacture.

It becomes impractical to order mill runs of titanium, and even with themill run production of optimum tubing dimensions, some undesirable costsremain. Due to many factors, technical and historical, it is verydifficult to force standardization in such a way as to significantlyincrease the quantities of any given configuration. At the same time,the standardization that has occurred has hampered alternateconfigurations even when there is a legitimate reason for suchconfigurations. For example, space may be too limited to install acrystal of a desired standard size because a standard package is toosmall. To design a smaller package results in an overall reduced levelof standardization and higher cost. To increase standardization suchthat it will reduce cost while, at the same time, allow variations whenneeded, requires making a standard design adaptable to be able to fitother designs.

By using thin windows and thin couplers, and by using the combinedeffect of the axial restraint of the flexible sleeve with a shorterspring, the length of a scintillation package can be made smaller toallow a given crystal package to fit into a smaller space in the machineor tool in which it is to be used. Then, by using an end cap (or end capadapter) on the rear that is adjustable in length, the same crystalpackage can be extended to fit snugly into a longer cavity in adetector, machine or tool. Therefore, the shortened shield can be usedfor any length of package, including package lengths that are somewhatshorter than would be considered standard and readily available. As aresult, larger batches of shields can be processed to a singleconfiguration, relying upon a simple end cap adapter to modify thelength of the finished product. These shields can be processed throughsapphire brazing in larger batches as well. A smaller than standarddiameter shield is proposed as a way to ultimately reduce cost. It isalso a way to allow small adjustments to the diameter of the package byapplying metallic tape or foil of various selected thickness. Since suchtape is readily available in different thicknesses, the finisheddiameter of the shield can be cheaply and quickly adjusted to match therequirement.

The above concepts may be extended to the entire detector assembly,i.e., to the combination of the scintillation package with aphotomultiplier tube.

As explained above, there is a need for a more space efficient methodfor supporting a complete PMT/crystal assembly, hermetically sealedwithin a single tube or shield and to make the PMT/crystal operable forlonger times at elevated temperatures. This can be accomplished by thefurther use of a thin flexible support sleeve, of polygon-shaped crosssection in the exemplary embodiment, which is placed around the entirePMT/crystal assembly. The PMT/crystal, along with the flexible sleeve,are hermetically sealed within a tube or shield that also extends thefull length of the PMT/crystal assembly.

In addition to providing mechanical support, such that the PMT andcrystal can be directly coupled with no window between them, theflexible metal support sleeve provides for highly damped, dynamicisolation from externally induced vibrations and shock in the radialdirection.

Dynamic support in the longitudinal direction consists of axial springmeans at each end of the PMT/crystal sub assembly, in combination withthe flexible metal support sleeve that extends over both components. Theflexible metal sleeve provides for a high resonant frequency in thelongitudinal direction, which prevents dynamic coupling with the highlevel, lower frequency, induced vibrations. As will be made clearer indetailed descriptions to follow, the flexible sleeve restrains thePMT/crystal assembly in the longitudinal direction through contactfriction. Under high shock conditions, the PMT/crystal will slide withinor relative to the flexible sleeve. When this happens, the slidingfriction produces a high level of damping which prevents the supportfrom amplifying the induced vibration. Also, by properly sizing aflexible sleeve, the PMT/crystal assembly can be held essentially rigidduring most induced vibration but released under shock or high vibrationto provide dynamic isolation where needed most.

Provisions are also made for the scintillation element or crystal toexpand, due to temperature increases, in both the radial andlongitudinal directions. In one embodiment, a reflector/support assemblythat lies between the crystal and the flexible sleeve comprisesreflective tape and a sidewall axial restraint and compliance Assembly(SARCA), as will be detailed later. Another embodiment uses reflectivesupport rings around the crystal with reflective materials between.These reflective rings then carry the loads between the scintillationelement and the flexible sleeve. In another embodiment, an oil ringedoptical coupling is used to improve light transfer at the PMT/crystalinterface, reduce spontaneous noise generations due to relative motionbetween the crystal and PMT, and to do so in a minimum amount of space.

During operation, high vibration or shock will cause the PMT/crystalsubassembly to slide within the flexible sleeve. This sliding frictionprovides effective damping. The coefficient of thermal expansion of theflexible sleeve is of little consequence in the radial direction sincethe flexible sleeve is only a few thousandths of an inch thick anddeflects to allow thermal compliance.

Support of the PMT, radially inward of the hermetic tube or shield andflexible sleeve, is accomplished by placing it in a PMT housing that hasthe same diameter as the crystal reflector and/or SARCA. Between the PMTand its housing is a plurality of circumferentially spaced, radialsprings or, preferably, another flexible sleeve to provide dynamicisolation for the PMT.

One critical aspect of support is to minimize bending of the PMT/crystalcombination in order to prevent damage to the optical coupling betweenthem, to prevent noise resulting from flexing the optical coupling, andto minimize bending modes in the assembly. This is also achieved by thepolygon-shaped flexible metal support sleeve that engages the exteriorof the PMT/crystal and the interior of the hermetic tube or shield, andthat is relatively stiff even though it is made from thin metal.

Since the PMT requires high voltage for operation and since it outputselectrical pulses it is necessary to provide electrical connectionsbetween the PMT and electrical circuitry outside the hermetic tube orshield, but still inside the detector. This is accomplished by use of aspecial feed through. Tool space can be further saved by addingelectronic components to the detector to avoid having additionalhousings available for that use. Described in one embodiment is apre-amplifier assembly that is located within the detector assembly,though not inside the hermetic tube.

Outside the nuclear detector, a flexible dynamic housing includingaxially extending radial springs or another (i.e., outer) flexible metalsupport sleeve provides still another level of dynamic support for thetotal detector assembly and provides mechanical compliance so that themechanical tolerances of the tool cavity, into which the detector is tobe placed, do not have to be as stringent. Although movement of thedetector is allowed by this outer flexible support sleeve, it onlyallows such movement within certain design parameters as will bedescribed in detail later. Longitudinal positioning and restraint of thedetector is accomplished with an elastomeric dome or end plug on eachend of the detector, in combination with the outer flexible sleevethrough sliding friction. The flexible dynamic housing may beconstructed, as disclosed in pending application Ser. No. 10/028,430filed Dec. 28, 2001. Also, a dual flexible sleeve may be used. Variousdynamic responses can be achieved through the detailed design of thesesupport devices around the detector, as will be explained later.

Various end cap adapters are also disclosed herein for adapting thedetector to different applications.

A detector package is also presented in which there is a standardizedcore assembly (comprising, e.g., a crystal and PMT and surroundingshield) that has been intentionally made slightly smaller in diameterthan the typical diameters being used, as well as shorter in length thanis typically required for a standard increment of crystal size. One orboth of the end caps of the core assembly may have a standardizedthreaded hole, having a relatively large diameter, shallow depth andfine threads. Metallic wraps or metallic flexible sleeves are sized toallow adjusting the diameter of the core assembly to fit a wide range oftool cavity or housing sizes. Use of flexible sleeves allows providingfor either a hard mounted configuration in order to maintain a dynamictransmissibility near unity for the expected vibration levels, or toprovide for dynamic isolation at higher frequencies. Use of end adaptershaving a standardized, short, threaded stud that matches the shallow,large diameter, threaded hole on the core allows the length of the coreassembly to be adjusted to fit a range of cavities sizes used in theapplication of use. End adapters also are provided with a selection ofconfigurations in order to mate with various configurations in themining machine, drilling tool, or other device into which the detectoris being installed. Taken collectively, a few standardized coreassemblies which contain detecting elements of a range of incrementalsizes can be adapted to numerous configurations. Standardizing allowsmanufacture and stocking of standardized cores at lower cost for use bya wide range of users, simply by adding adapters as needed.

Accordingly, in one aspect, the invention relates to an instrumentationpackage comprising at least one substantially cylindricalinstrumentation component; a substantially cylindrical shieldsurrounding the at least one instrumentation component, the shieldhaving a diameter less than a standard predetermined diameter; and asizing sleeve around the shield, thereby increasing the diameter of thesleeve to the standard predetermined diameter.

In another aspect, the invention relates to a nuclear detector packagecomprising a substantially cylindrical nuclear detection element; asubstantially cylindrical shield surrounding the nuclear detectionelement, the shield having a diameter less than a standard predetermineddiameter; and a sizing sleeve around the shield, thereby increasing thediameter of the sleeve to the standard predetermine diameter.

In still another aspect, the invention relates to a radiation detectorcomprising a substantially cylindrical crystal element; aphotomultiplier tube arranged coaxially with the crystal element; anoptical coupler sandwiched between one end of the crystal element and anadjacent end of the photomultiplier tube; the crystal element, opticalcoupler and photomultiplier tube hermetically sealed within acylindrical shield; and a flexible support sleeve extending exteriorlyalong the crystal element and the photomultiplier tube and radiallyinside the cylindrical shield.

In still another aspect, the invention relates to a radiation detectorcomprising a substantially cylindrical crystal element; aphotomultiplier tube arranged coaxially with the crystal element; anoptical coupler sandwiched between one end of the crystal element and anadjacent end of the photomultiplier tube; the crystal element, opticalcoupler and photomultiplier tube hermetically sealed within acylindrical shield; a non-hermetically sealed electronics housingadjacent the photomultipler tube for electrical components electricallyconnected to the photomultiplier tube; wherein the photomultiplier tubeis mounted within a PMT housing inside the cylindrical shield, with aflexible metal sleeve radially between the PMT housing and the shield.

The invention will now be described in detail with reference to thedrawings identified below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side section of a scintillation package in accordance withthe invention;

FIG. 2 is a cross section taken along the line 2—2 of FIG. 1;

FIG. 3 is an enlarged detail taken from FIG. 1;

FIG. 4 is an enlarged detail taken from FIG. 1;

FIG. 5 is a side elevation, partly in section, of a highly integratedgamma detector in accordance with an exemplary embodiment of theinvention;

FIG. 6 is an enlargement of a center portion of FIG. 5;

FIG. 7 is a section taken along the line 7—7 of FIG. 5;

FIG. 8 is a section taken along the line 8—8 of FIG. 5;

FIG. 9 is a section taken along the line 9—9 of FIG. 5;

FIG. 10 is a partial section of a detector assembly located within atool housing in accordance with another embodiment of the invention; and

FIG. 11 is a partial section illustrating a variation in an end adapterin accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference initially to FIGS. 1–5, a nuclear detector package 10 inaccordance with an exemplary embodiment of the invention includes ahermetically sealed housing or shield 12 containing an instrumentationcomponent, in this case a nuclear detection element in the form of ascintillation or crystal element 14, a reflector 16 surrounding thecrystal element, a support sleeve 18 for supporting the crystal elementwithin the shield, and a window 20 and optical coupler 21 through whichlight from the scintillation element passes to the outside (e.g., to aconnected photomultiplier tube). Critical to reliable and noise-freeperformance in the harsh environments in solid mineral mining or oilwell logging, is the support structure for the scintillation or crystalelement 14. If not done properly, the crystal will move under highvibration or shock and may produce noise, break or otherwise fail. Thisis particularly true for MWD and LWD applications, but is also aconsideration for wireline applications (Wireline, in the oil welllogging industry, refers to the lowering instrumentation packages into aborehole and then making measurements of the formation and/or conditionof the bore hole during removal).

In the exemplary embodiment, the dynamic support arrangement for thescintillation or crystal element 14 comprises a flexible support sleeve18. Use of this support sleeve 18 also creates opportunities for otherimprovements. As best seen in FIG. 2, the flexible support sleeve 18inside the shield 12 has a polygon shape in cross section. Specifically,the illustrated sleeve 18 is generally in the shape of a cylinder, butwith five flat surfaces or flats 22. The dimensions are selected suchthat these flat surfaces 22 press against reflector material 16 (such asa conventional Teflon® tape) that is applied around the scintillationelement 14. The thickness and type of material used to make the flexiblesleeve 18 are selected in order to support the scintillation element 14so as to achieve a minimum natural frequency. The sleeve 18 ispreferably metal (e.g., stainless steel) but could be made of otherappropriate material. The number of flats 22 may vary, combined with theknowledge of the space between the scintillation element 14 and theinterior wall of the shield 12, determines the amount of preload on thesurface of the scintillation element 14. A lubricating coating 24 (FIG.2) on the interior surface of the flexible support sleeve 18, incombination with the preload force on the crystal element 14 determinesthe amount of axial restraint due to the friction between the flats 22and the outer surface of the reflector material 16. The configuration ofthe flexible support sleeve 18 uses very little space, thus freeing upspace for a larger crystal 14, if desired.

A small radial step 26 (see FIG. 4), only about 0.005″ high, can beprovided on an inner surface of the shield 12 so that the flexiblesupport sleeve 18 will be stopped from sliding forward (toward thewindow 20). By making the flexible sleeve 18 shorter than the crystal14, the flexible sleeve 18 will not extend over the crystal 14 in thefront portion (near the optical coupler 21 of the crystal 14). Thoughsuch partial support may be less acceptable for the most extrememeasurement while drilling applications, having the crystal 14cantilevered inside the flexible sleeve 18 is feasible for solid mineralmining and wireline applications. In this fashion, there is nocompression of the reflector tape 16 in the front portion of the crystal14, thus reducing absorption of light. This radial step 26 also makes itpractical to utilize a precision reamer tool to simply and cheaplycomplete the machining of the area to be brazed to the window 20.

Similarly, at the rear of the crystal 14, the reflector tape 16 aroundthe crystal is not compressed, which improves reflectivity and helpslight to press from the rear of the scintillation crystal 14 to thewindow 20 more effectively. Further, since the portion of the reflectortape 16 at the rear of the crystal 14 is not compressed, a thinreflective pad 28 at the rear of the crystal 14 can be simplyconstructed and installed by allowing the edges and/or corners of thepad 28 to overlap onto the cylindrical surface of the crystal 14. If thereflector tape in the end region of the crystal 14 were compressed, thenthe overlapping material from pad 28 would make the reflector tape 16thicker in this region, causing it to be compressed even more. Evenworse, the crystal 14 would likely expand toward the rear during hightemperature operation, then get stuck in that position. As the crystal14 cools down, the front end of the crystal would pull away from thecoupler 21. This is a well known problem. The current invention allowsthe overlap which is desirable for higher performance and simpler andlower cost without the risk of the crystal 14 getting stuck at the rear.In order to restrain the flexible sleeve 18 against the step 26, a thinpositioning sleeve 30 is installed at the rear of the flexible sleeve14, between the back edge of the sleeve 18 and the end cap or back plate38.

Since it is not practical to standardize the diameters and lengths andtolerances for all ruggedized crystal packages, even being undesirablein many instances, if cost reduction is to be achieved bystandardization, it must be accomplished in another way. By makingstandard shields that are smaller in diameter, the diameter can then beincreased by adding a sizing sleeve or metal wrap 32 that extendssubstantially the full length of the shield, and that has the requiredthickness to achieve the specified diameter to within a specifiedtolerance. By using this method, very precise diameters can be achieved,as is desired by some tool manufacturers, and can be done at a greatlyreduced cost over trying to machine to satisfy the tolerances.

For example, if a 1.249 inch diameter stainless steel scintillationpackage is needed with a tolerance of ±0.001″, the shield 12 would beturned at a smaller size, such as 1.240″±0.003″. Once complete, if thediameter measures 1.243″, a sizing sleeve 32 made from standard 0.0015″metal foil material can be applied, using a suitable bonding material.If the measured size of the raw shield is 1.237″, then a sizing sleeve32 made from 0.004″ stainless steel would be bonded to the shield.Sizing rings (not shown), having an I.D. of 1.249″ may be slipped overthe top of the sizing sleeve 32. After the bonding material cures, thesizing rings would be removed. Other combinations of machined sizes,sheet material used for sizing sleeves, and bonding materials may beused, depending upon process preferences and cost considerations. Forexample, in order to have a much higher degree of standardization suchthat packages requiring slightly smaller finished package diameters needto be fabricated from the same standard raw shield size, the shields maybe machined to a standard diameter of 1.235″±0.003″. Starting with thisstandard shield 12, having a nominal 1.235″ diameter, a finisheddiameter of 1.245″± can be achieved by use of a sizing sleeve 32 of0.003″. But starting with this same shield 12, the diameter can beprecisely controlled to 1.249″ by using 0.005″ sizing sleeve material,applied with sizing rings, as described above.

It will be appreciated that other techniques are possible for preciselysizing the shield. For example, rather than a metal foil wrap bonded tothe undersized shield, tape with a suitable adhesive backing, could beused to achieve the desired diameter. More significantly, a flexiblemetal sizing sleeve of polygon shape, similar to support sleeve 18, canbe employed to allow the otherwise undersized shield fit precisely in astandard tool housing. By use of the flexible sizing sleeve, a fullrange of dynamic support options are created. A relatively stiff sleevecan be employed, using a relatively high frictional loading, so as tohold the detector fixed under most expected vibration conditions. Usingthe option, the detector will not resonate at the frequencies of theinduced vibrations. A dual flexible sleeve may be used in order toprovide a high degree of isolation without a significantly highresonance and still retain a high level of shock isolation. Anotheroption is to use a sleeve of moderate stiffness and moderate frictionalloading that produces dynamic isolation over higher frequencies anddamped resonance in a frequency range where there is less concern.

Another important consideration for assuring low failure rates and lowercost for brazing sapphire windows onto thin sleeves is to ensure thatthe shield is round. Once shields are machined to standard smallerdiameters, they can be held round by use of sizing collars, made fromthe same material as the shield 12, that are installed prior to brazing.

There is some standardization of crystal length for ruggedizedscintillation packages. Typical lengths are in multiples of inches. Forexample, a 4″ in length×1″ in diameter size has been popular for manyyears. Diameters of scintillation crystals 14 and scintillation packages10 typically vary by increments of ⅛ inch so that ⅞×4 and ¾×4 crystalsizes are also commonly used sizes. In recent years, there has been atrend to use smaller diameter, longer length crystals due to the limitedspace within tools or machines.

By choosing the shortest crystal package that is feasible for standardcrystal sizes, an end cap adapter assembly with an extender section (ora removable spacer) allows a single package size to fit a range ofcavities by simply changing the end cap or even better, by changing thesize of spacer used on the end cap. Referring to FIGS. 1 and 3, an endcap adapter 34 with an extender section or spacer 36 work in concertwith the end cap or back plate 38, and may vary the length of thepackage 10 over a typical range of 0.6 inches (obviously, the spacer 36could be longer or shorter as needed. However, most packages containinga 4 inch long crystal will vary in length from 4.4 inches to 5 inches.In addition to varying the size of the spacer 36 to alter the effectivelength of the package, another option is to make the end cap spacer 36from two or more smaller parts. Or, the spacer itself may also functionas an end adapter. The end cap adapter 34 may also have whatever endfitting configuration required, such as, for example a threaded stud,threaded hole, boss or pin, spindle, etc., some of which are describedfurther below. Crucial to this concept for standardization is astandardized interface on the end cap 38 and a matching interface on theend adapters (34 and/or 36).

As assembled, a compression plate 40 is located against the reflectivepad 28 and an axial spring 42 is interposed between the compressionplate 40 and the end cap or back plate 38. Note also that the shield 12is welded about its back end to the periphery of the end cap 38. Thepositioning sleeve 30, located axially between the end cap 38 andflexible sleeve 12, is fitted with a nominal gap therebetween to allowfor slight adjustment of the sleeve. An assembly screw 44 extendsthrough the end cap adapter 34 and spacer 36 and is threaded into theback plate or end cap 38.

At the forward end of the package (see FIG. 4), a reduced diameter endportion 46 of the shield 12 is brazed to the window 20, with a siliconerubber (or other suitable material) spacer 48 located about the coupler21 and axially between the window 20 and the reflective material or tape16 wrapped about the crystal 14.

Coupling of the scintillation or crystal element 14 to the window 20 maybe accomplished by molding or by bonding with a relatively thin couplingmaterial made from optically transparent materials such as SYLGARD®,which has frequently been used for this purpose. Using a ringed pad inorder to retain a coupling oil on its surface greatly improves thequality and durability of the optical coupling. This so-calledoil-ringed coupler also helps to reduce mechanically induced noise. Thethin optical coupler 21 is made more effective under high dynamicconditions through the use of the flexible support sleeve 18. Theflexible support sleeve 18 provides positive restraint in the axialdirection so that the scintillation element 14 does not easily moveunder high vibration, and provides a high natural frequency in the axialdirection. If shock or vibration becomes high enough to cause thescintillation element or crystal 14 to slide within the flexible supportsleeve 18, the sliding effectively dissipates energy through slidingfriction which quickly dampens the motion. Yet, allowing the crystal 14to slide some during high vibration or shock, or due to high temperatureexcursions prevents high forces from building up in the assembly. Thisis in contrast to relying on elastomers which tend to flex in the axialdirection under low levels of vibration or shock, allowing thescintillation element 14 to resonant, thus further increasing thedynamic forces. This build up of resonance is damaging and/or producesnoise in the output. Since the flexible support sleeve 18 is very rigidin the axial direction, the high natural frequency prevents dynamiccoupling with externally induced vibration so that resonance is lesslikely to start. Then, if the levels of induced vibration or shock arehigh enough to cause the scintillation element to begin moving, it isquickly damped out by sliding friction, as explained earlier.

A gamma detector used in mining usually consists of a scintillationpackage (which produces flashes of light when struck by gamma rays) incombination with a light detecting device that converts the lightflashes to electrical pulses. Most often, the scintillation element is athallium activated sodium iodide crystal and the light detecting deviceis a photo-multiplier tube (PMT). When using hygroscopic crystals, suchas sodium iodide, both components must be shielded from moisture,including moisture in air. Gamma detectors are typically constructed byenclosing the hygroscopic crystal in a hermetically sealed tube orshield which contains a window through which scintillation light pulsespass to the PMT. This window can be eliminated, however, by includingthe PMT inside the hermetic housing. Elimination of the window, as hasbeen done in this preferred embodiment, improves the transfer of lightfrom the crystal into the PMT.

With reference now to FIGS. 5 and 6, a radiation (e.g., gamma ray)detector 50 in accordance with an exemplary embodiment includes ascintillation element or crystal 52 and a photo-multiplier tube (PMT) 54which are hermetically sealed within a tube or shield 56.

The crystal 52 and PMT 54 are directly coupled, with no windowtherebetween, by means of an optical coupler 58. Directly coupling thecrystal 52 through the optical coupler 58 requires solving variousengineering problems, particularly for a detector that is to be used ina harsh environment. Necessary actions include making special provisionsfor how the crystal 52 and the PMT 54 are supported within the tube orshield 56 and other important considerations.

In this exemplary embodiment, the crystal 52 is positioned in one end ofthe shield 56 with the PMT 54 and the optical coupler 58 at the otherend. The end of the shield 56 in which the crystal 52 is placed issealed with an end plug 60. The PMT end of the shield 56 is madehermetic by a feedthrough 62. An electrical divider string 64, shown inFIGS. 5 and 6, necessary for the PMT 54 to function, is included in thehermetically sealed portion of the shield 56. Electrical power to thedivider string 64 and the signals from the PMT 54 are passed through thehermetically sealed feedthrough 62. In this particular embodiment, apreamplifier assembly 66 is included in the electronics housing portion68 of the detector 50 that is not hermetically sealed. The preamplifierassembly 66 may be supported by axially extending radial springs 70 (seeFIG. 8) between it and the housing 68, or, alternatively, by a flexiblesupport sleeve. Other electronic components located in the housingportion 68 may include a PC board mount 72, a power supply, digitalprocessing electronics, or other electrical components that may be of aconventional nature, with exit wires 76 extending out of the detector.

When a gamma ray produces a scintillation flash in the crystal 52, lightemanates from the point of scintillation in all directions. Efficientoperation of the detector 50 requires that the light produced by thescintillation element or crystal 52 that goes in directions other thantoward the PMT 54 must be reflected toward the PMT. In this embodiment,the reflector consists of reflective TEFLON® tape that has been wrappedaround the cylindrical portion of the crystal 52 and a reflective disk74 on the end of the crystal 52 remote from the PMT 54. This disk 74 maybe constructed from various materials, including alumina. An alternativeto the disk 74 is a pad made from multiple layers of the reflective tapematerial used around the cylindrical portion of the crystal 52. Theamount of reflection from certain areas of the crystal 52 is increasedby changing the features on the surface of the crystal. For example, itis common practice to sand or scratch the crystal surfaces in regionsaway from the PMT 54 to improve the diffuse reflection of light towardthe PMT.

Efficient transfer of light from the crystal 52 to the PMT 54 requiresthe optical coupler device 58, shown here as an oil-ringed couplerfilled with optical coupling fluid, preferably a silicon oil. Thiscoupler 58 is preferably a Sylgard® pad capable of carrying substantialaxial loading, and has been molded onto the face plate 82 of the PMT 54and, when feasible, onto the PMT housing 78 that surrounds the PMT.Another method for coupling is to bond the end 80 of the crystal 52 tothe faceplate 82 of the PMT 54. Another method for coupling may be anoil-ringed coupler having oil retaining rings on both surfaces of thecoupler 58.

When noise-free operation is required under extreme vibrationconditions, such as certain MWD operations where vibration levels mayreach 40 G rms, additional support provisions are required. In thisembodiment, the PMT 54 is enclosed within the PMT housing 78, includinga front portion 84 and a rear portion 86. The front portion 84 extendsbeyond the PMT 54, overlapping the optical coupling interface betweenthe PMT 54 and the crystal 52. The remote end of the front portion 84 isformed with circumferentially spaced slots 88, while an annular gap 90lies forward of the slotted end of the front portion 84. In other words,the front portion 84 of the PMT housing is slidably received over areduced diameter portion 92 of the crystal 52, with the gap 90 axiallybetween the PMT housing and a tapered shoulder 94 on the crystal 52. Ametallic band 96 coated with a lubricating reflective material or othersuitable reflective, low friction material, is located on the reduceddiameter portion 92 of the crystal for reasons provided further herein.

The front portion 84 of the PMT housing 78 is formed with progressivelyincreasing diameters from a first inner diameter at 98 to a second innerdiameter at 100 and a third inner diameter at 102. The first innerdiameter 98 is sized to create a radial space between the PMT 54 and thehousing 78 that is filled with a silicon-based rubber material 104 knownas RTV. This material prevents leakage of Sylgard® while being moldedonto the face of the PMT 54.

The second inner diameter 100 is sized to permit the insertion ofaxially extending, circumferentially spaced radial strip springs 106(typically stainless steel) radially between the PMT 54 and the PMThousing 78. These springs 106 extend along a major portion of the lengthof the PMT, terminating at a tapered shoulder 108 at the rear end of thePMT 54. For a one inch diameter detector, the springs may be about 0.005inches thick and 0.37 inches wide. Other sizes may be selected to alterthe resonant frequency and other properties thereof. The PMT springs 106may be replaced by another flexible, polygon-shaped sleeve, similar tothe sleeve 120 described further herein.

The third inner diameter 102 is sized to permit insertion of a splitring 110 and a plurality of annular shims or spacers 112 that preventslide-back of the PMT. This arrangement also provides the capability forusing PMT's of different length, i.e., shims may be removed or added asrequired to accommodate a PMT of increased or decreased length(indicated in phantom in FIGS. 1 and 2).

The rear portion 86 of the PMT housing has a reduced diameter end 114that is telescopically received within the front portion 84 of thehousing 78. The opposite end of the rear portion 86 is counterbored toreceive an end cap 116. RTV material 118 partially fills the spacebetween the end cap 116 and the divider string 64.

One critical need for supporting the fragile crystal 52, often made frommaterials such as sodium iodide which is easily broken, and the PMT 54is to prevent bending of the assembly, particularly in the area aroundthe optical coupler 58. If bending is allowed, light pulses will oftenbe generated under high vibration due to movement of the materials. Ifthe interface consists of bonding the PMT 54 together with the crystal52, using a transparent coupling material, for example, the coupler 58,this bond may actually be broken. Unfortunately, these problems existfor even very small amounts of bending resulting from little relativemotion of the crystal 52 relative to the PMT 54. Bending is prevented byinstalling a thin, polygon-shaped, flexible support sleeve 120 aroundthe PMT/crystal assembly. This sleeve is preferably metallic but couldbe made from other high strength materials that exhibit springcharacteristics. Referring again to FIG. 5, the flexible support sleeve120 is located radially inside the hermetic tube or shield 56, andsurrounds the crystal 52. This flexible support sleeve 120 (see alsoFIGS. 6 and 7) has a polygon-shaped cross-section and is relativelystiff even though the metal is thin (in the range of from 0.002″ to0.005″). In the embodiment shown, the flexible sleeve 120 has 10 flatsides, each of which has a width of about 0.28 inches. Each flat side orsurface 134 engages the outside surface of a radial and axial supportassembly 122 that surrounds the crystal, and the outside surface of thePMT housing 78. Corners 136 defined by the flat surfaces 134 engage theinner surface of the hermetic tube or shield 56. As a result, theflexible support sleeve 120 is effective for minimizing bending betweenthe PMT 54 and crystal 52. The diameter of the PMT housing 78 around thePMT 54 and the crystal 52 (including supporting materials discussedfurther below) are made to be substantially the same so as to producecontact along substantially the full length of the flexible supportsleeve 120.

The crystal 52 is wrapped with a TEFLON® or other suitable reflectivetape (the outer surface of the tape may have a polyamid layer thereon).The crystal is supported by the radial and axial support assembly 122.The support assembly may comprise a sidewall axial restraint andcompliance assembly, or SARCA, of the type disclosed in U.S. Pat. No.5,962,855. The SARCA generally includes an inner polyamide sleeve and anouter stainless steel sleeve or wrap, the interfacing outer surface ofwhich may be coated with Teflon®. Note that the SARCA is axially shorterthan the crystal at one end thereof closest to the optical coupler 58that is located between the crystal 52 and the PMT 54, such that it doesnot limit any axial movement of the PMT housing 78. Similarly, length ofthe flexible sleeve is less than the combined length of the PMT/crystalassembly for the same reason.

The support assembly 122 may, in an alternative arrangement, includeannular support rings over the top of the reflective Teflon® tape, withadditional layers between the rings. The first mentioned SARCA supportassembly is especially useful in MWD operations, while the secondmentioned support assembly is especially useful in Wirelinearrangements. It will be understood that the SARCA arrangement may alsobe employed in the package shown in FIG. 1, located radially inward ofthe flexible support sleeve 18.

The crystal end of the hermetic tube 56 is closed by the end cap or plug60 with an axial spring 124 interposed between the end plug and thereflective disk 74 on the back end of the crystal. The PMT end of thehermetic tube 56 is sealed by the feedthrough 62, with axial spring 126interposed between the feedthrough and the end cap 116. Thus, springs124 and 126 bias the PMT 54 and crystal 52 toward each other,maintaining compressive engagement at the coupler 58. The axial forcesgenerated by springs 124, 126 are determined by the sizing of thesprings, differential thermal expansion and dynamic forces. The forcesrequired by these springs 124, 126 are greatly reduced by the use of theflexible sleeve 120. The flexible sleeve provides a specified axialrestraint that increases at a predictable rate that is much less thanwould be produced by a non-linear elastomeric support.

Surrounding the hermetic tube or shield 56 is another radial supportassembly, herein referred to as a flexible dynamic housing 128 that mayinclude a plurality of axially extending metal springs 130 within athin, outer flexible metal sleeve 132. The sleeve 132 may be constructedby rolling a sheet of stainless steel 0.0015 inches thick to produce twocomplete layers, bonded with high temperature adhesive. In analternative arrangement, the springs 130 may be replaced with an outerflexible metal support sleeve of polygon cross-section, similar tosleeve 120. The flexible dynamic housing (including springs 130 or outerflexible sleeve) extends the full length of the detector, extendingbetween end plug 60 at the crystal end of the detector and end plug 142at the opposite end thereof.

As already mentioned, the outer surfaces of the cylindrically shapedsupport assembly 122 and the outer surfaces of the PMT housing 78 are incontact with the flat portions 134 of the flexible support sleeve 120,while the corners 136 of the flexible sleeve 120 are in contact with theinner surface 138 of the hermetic tube 56. Whenever external forces areapplied to the tube 56 so that it begins to accelerate in the directionof the applied force, the inertia of the crystal 52 will result in theflexible support sleeve 120 moving relative to the crystal 52 so that aforce is applied to the flexible support sleeve 120 at the flat surfaces134 and corners 136 of the sleeve. The flexible support sleeve 120 willbegin to bend around the points of contact and will increase forceagainst the crystal 52 and thereby accelerate the crystal.

The amount that the flexible support sleeve 120 bends and the rate thatthe crystal 52 is accelerated is dependent upon the force being appliedand the stiffness of the flexible sleeve. As the flexible sleeve 120 isbent by the force being applied to it, the result is that the corners136 must slide on the inner surface 138 of the tube 56 into which it isinstalled. Also, the crystal 52 must slide relative to the flat surfaces134 of the flexible support sleeve 120 in order to move relative to it.The configuration of the flexible support sleeve 120 is such that thecontact pressure increases as the deflection increases so that thefriction component is proportional to the radial movement. Both of theseactions, sliding of the support sleeve 120 relative to the tube orshield 56 into which it is installed and sliding of the detector 50(i.e., the PMT/crystal) relative to the support sleeve 120, producesvery beneficial damping due to the sliding friction. This is in contrastto spring means such as elastomers which typically do not slide muchrelative to the other surfaces but deform. The damping from deformingsuch materials is limited to the internal losses of the materials asthey are distorted. Such internal losses are not as effective forproducing damping as a design having sliding friction, such as aflexible sleeve. A high level of damping is extremely beneficial becauseit minimizes the response to high levels of vibration and shock.

Thermal expansion is a critical parameter in the design of a nucleardetector being used downhole because the temperature often is as high as175 Degrees Centigrade and may even be as high as 200 DegreesCentigrade. As the PMT housing portions 84, 86 expand, relative to theglass envelope 140 of the PMT (see FIG. 5), the PMT springs 106 (orsuitable flexible sleeve) relax but stay in contact with the PMT housingportions 84, 86 and the PMT 54. As the PMT housing portions 84, 86typically made from poly-ethyl-ethyl-ketone (PEEK), expand outward, itis at approximately the same rate as the crystal element 52 expands.This expansion of the housing portions 84, 86 and the crystal 52 isaccommodated by the flexible support sleeve 120. As the support sleeve120 is compressed, the force from it on the housing portions 84, 86 andthe crystal 52 increases but at a constant and predictable rate. Beingmetallic, the stiffness of the flexible support sleeve 120 does notchange significantly as a result of being loaded by the expansion of theitems being supported so that the natural frequency of the supportedelement does not change by a significant amount. A temperature increasefrom room temperature to 175 degrees Centigrade produces a relativeexpansion of about 0.0046 inches. Given the spring properties of theflexible metal support sleeve 120, the amount of expansion of the PMThousing portions 84, 86 and the crystal 52 is relatively small.

During operation, vibration and shock in the radial direction will alsoresult in the flexible sleeve 120 being deflected. Ideally, the supportsleeve 120 would be deflected equally at the PMT 54 and at the crystal52. However, since the mass density of the two are different, there willbe a small difference. For measurement while drilling (MWD)applications, this difference, may, at times, cause enough relativemotion at the coupler 58 between the PMT 54 and the crystal 52. Wheneverthe coupler 58 is molded to the faceplate 82 of the PMT 54, as in thisembodiment, the relative motion will occur within the optical coupler 58but most of the relative motion will occur at the interface between theoptical coupler 58 and the face end 80 of the crystal 52. Fortunately,the oil on the surface of the oil-ring coupler will allow some freerelative motion without producing flashes of light which would beinterpreted by the PMT 54 as a scintillation, giving a false reading.Also, small relative motions will not cause a loss of oil from betweenthe rings on the coupler 58. However, under the most severe conditions,the relative motions may be detrimental to the operation of the opticalcoupler 58. To prevent this from happening, portion 92 of the PMThousing has been extended beyond the face of the crystal 52 in order tocapture the end of the crystal 52. As already noted, if the diameter ofa crystal 52 is larger than the diameter of the PMT, as shown in FIG. 1,the diameter of the front end of the crystal 52 is reduced to allow thePMT housing 78 to extend over the reduced diameter portion 92. Highreflectivity is retained for this portion of the crystal 52 by placingthe metallic band 96 around the reduced diameter portion 92 of thecrystal 52, i.e., in the region that is captured by the PMT housing 78.This band is coated with a suitable white, reflective coating, such as acombination of alumina and boron nitride. Such a coating is also alubricant so that the crystal 52 is free to slide within the housing 78.A layer of reflective Teflon® tape may also be used in place of thisband. The lubrication on the band is important to prevent the crystal 52from getting stuck, during thermal cycling, in a position slightly awayfrom the coupler 58 such that oil might escape. Thus, the arrangementprovides a “slip joint” that allows the PMT 54 and crystal 52 to moverelative to each other in an axial direction but restrains motion in theradial direction. This may occur when the optical coupler 58 expandswith temperature and pushes the crystal 52 away but then contracts withlowering temperature. Given the relatively linear stiffness of theflexible sleeve, the radial compressive forces are kept sufficientlylow.

In instances where the diameter of the PMT 54 is nearly as large as thecrystal 52, there is no space for the added support of the PMT. In thatcase, the PMT may be sized to be in direct contact with the flexiblesupport sleeve 120. This may be accomplished by wrapping the PMT with asheet of thin, strong material, such as stainless steel. In order toprovide the support of the crystal at the PMT/crystal interface, thewrap may be extended over the front of the crystal.

Thus, the incorporation of flexible support sleeve 120 and otherconstruction features described herein provide uniform support, dynamicisolation and axial restraint for the PMT/crystal assembly within thedetector 50, all in a predictable and controlled manner.

FIG. 10 represents another highly integrated detector construction inaccordance with the invention, located within an external tool housing.Specifically, the detector 150 includes a scintillation or crystalelement 152 axially coupled to a PMT 154 via an optical coupler 156(preferably with oil filled rings). The crystal and PMT are hermeticallysealed within a tube or shield 158 that is welded at opposite ends,i.e., to an end cap or back plate 160 at the back of the crystal 152 anda front plate 162 at a forward end of the PMT 154.

A compression plate 164 and axial spring 166 are located axially betweenthe standardized back plate or end cap 160 and the crystal. An end capadapter or spacer 168 is located behind the end cap 160, with a spring170 between the end cap adapter 168 and an adjoining tool element 172.An end adapter spindle 174 is secured to the end cap 160, through thespacer 168, by means of a threaded stud 176 threadably secured to theshallow, relatively large diameter threaded socket 177 in the end cap.Note that the flat surface of the end cap 164 provides a matchinginterface for the spacer 168. Other matching surface configurations mayalso be employed.

At the forward end of the assembly, the forward end plate 162 encloseselectrical connectors 178 that project out of the assembly, but that arefurther enclosed within another end cap adapter 180 that includes acentrally arranged tubular extension or spindle 182 that guides andmaintains lead wires (not shown) attached to the connectors 178. Anannular spring 184 is located against a shoulder 186 of the end capadapter 180, sandwiched between the latter and another adjoining tool188. A first flexible support sleeve 190 is located radially between thePMT 154 and a PMT housing 192. A second flexible support sleeve 194 islocated radially inside the tube or shield 158, extending along the PMThousing 192 and a radial spacer 193 for the crystal 152. It will beunderstood that the crystal 152 may be wrapped with a reflective tape aspreviously described by a SARCA 195. This entire assembly is located ina cylindrical tool housing 196, with a third outer flexible supportsleeve 198 radially interposed between the hermetic tube or shield 158and the tool housing 196. It will be appreciated that the flexiblesupport sleeves 190, 194 and 198 are preferably metal and are alsopolygon-shaped in cross section.

It will be appreciated that flexible sleeves like sleeves 190, 194 and198 may also be used in connection with other radiation detectorconfigurations, as well as other, different kinds of instrumentationpackages, to provide radial and axial support for the instrumentationcomponents.

FIG. 11 illustrates yet another adapter arrangement including astandardized end cap 202 and threaded stud 200. In this arrangement, theextended spindle has been removed in favor of an axially shorter tip 204that allows incorporation of a radiation calibration source withoutotherwise changing the design of the adapter.

It will be appreciated that the standardized end caps may be providedwith various interfaces for securing matched adapters to meet specificrequirements.

Flexible support sleeves as described herein can be used in combinationsso as to optimize protection for various elements within aninstrumentation package, such as a nuclear detector. The PMT must besupported, the PMT/crystal has a combined support, and the completedetector must be supported. When operating within an extreme vibrationenvironment, possibly as high as 40 G rms or with frequent shocks above200 Gs, it may be important to provide different protections forelements within the package, by use of multiple flexible sleeves.Consider, for example, a scintillation detector of the type shown inFIG. 5. If this configuration were selected for use in a 40 G rmsvibration and high temperature environment at 175 Deg. C., protectionrequirements for the crystal assembly may differ from that for the PMTor the PMT/crystal combination. In order to prevent mechanical motionfrom generating optical flashes at the interface, or at the crystalsurfaces, the relative motion of the PMT and crystal must be kept verysmall. To achieve small relative motion, the flexible support sleeve 120that surrounds the crystal and the PMT must be relatively stiff, with aresonant frequency set at 500 Hertz or above, or the preload would beset so as to keep the PMT and crystal locked in position under vibrationbut releasing under high shock. If a second flexible support sleeve isused around the PMT (in place of individual springs 106), it wouldlikewise typically be relatively stiff with a resonant frequency about1000 Hertz. Given these two choices made, a decision would be made as towhether the outer flexible support sleeve would be configured to have atransmissibility of near unity over the expected frequency range or tohave a moderately damped resonance at some frequency that would providedynamic isolation for higher frequencies. One factor would be theexpected power spectral density over the range of frequencies expectedto be induced by the environment and the other would be the sensitivityof the PMT to high frequency. If a PMT is expected to be easily affectedor damaged by the higher frequencies, isolation might be chosen. Aresonant frequency around 700 Hertz would be chosen and preload would beselected to provide suitable damping at the maximum vibration level,chosen here as 40 G rms. The amount of damping and the amount ofisolation desired at the sensitive frequency would be selected foroptimum results. If, on the other hand, the induced vibrations are notexpected to have much energy at the higher frequencies or the PMT is notespecially sensitive to higher frequencies, the flexible support sleeve120 around the detector would be sized to provide adequate stiffness andpreload to keep the detector from moving, similar to being hard mounted,for the 40 G rms. Another example would be when operating in anenvironment in which most of the incoming vibration energy is below somefrequency, such as 400 Hertz, and the PMT being used is relativelyinsensitive to the lower frequencies. The flexible sleeve around thedetector would typically be sized to have a natural frequency at least1.4 times the maximum frequency, or 560 Hertz. By using this approach,the installation forces can be kept low since the approach is toseparate the natural frequency from the induced frequencies rather thanto hold the detector fixed through friction. Another example would bethe use of a detector configuration similar to that shown in FIG. 10which is to be used in a wireline application. Under vibration, thecrystal and PMT would be held fixed by the friction of the flexiblesupport sleeve 194 within the shield 158 for the moderately harshvibration wireline environment and the entire detector would also beheld fixed by friction with another, outer flexible support sleeve 198around the detector. Under shock, the outer sleeve would be the first tobreak friction to allow shock isolation, followed by the inner sleeveallowing movement for shock isolation. As can be seen from theseexample, flexible support sleeves can be configured to be used incombination to optimized dynamic support designs for a wide range ofcombined vibration, shock, and high temperature environments for avariety of sensitive instrumentation elements.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A nuclear detector package comprising: a substantially cylindricalnuclear detection element; a substantially cylindrical shieldsurrounding said nuclear detection element with a flexible metal supportsleeve radially interposed between and engaged with said nucleardetection element and said shield, said shield having a first diameter;a sizing sleeve around said shield sized to increase the first diameterto a larger second diameter; and a substantially cylindrical housing inwhich said detection element, shield and sizing sleeve are received,wherein said sizing sleeve adapts said detection element and said shieldto be received in said cylindrical housing.
 2. The nuclear detectorpackage of claim 1 wherein said flexible, metal support sleeve has apolygon shape in cross-section.
 3. The nuclear detector package of claim2 wherein said sizing sleeve comprises a second flexible metal sleevehaving a polygon shape in cross-section.
 4. The nuclear detector packageof claim 3 wherein said first and second flexible metal sleeves areconstructed of stainless steel.
 5. The nuclear detector package of claim2 wherein material and properties of said first flexible metal sleeveare chosen so that said first flexible metal sleeve exerts sufficientforce on said nuclear detector element to prevent said nuclear detectionelement from moving under normal levels of vibration but releases thenuclear detection element for movement under high shock.
 6. The nucleardetector package of claim 1 wherein said sizing sleeve comprises metalfoil bonded to said shield.
 7. The nuclear detector package of claim 1wherein said sizing sleeve comprises adhesively backed tape.
 8. Thenuclear detector package of claim 1 wherein said support sleeve isaxially shorter in length than said nuclear detection element.
 9. Thenuclear detector package of claim 8 wherein said shield is formed withan internal shoulder adapted to engage a forward edge of said supportsleeve.
 10. The nuclear detector package of claim 9 wherein said shieldis closed at one end by an end cap that is effectively adjustable inlength.
 11. The nuclear detector package of claim 10 wherein said endcap has a standardized interface for attachment to an end adapter. 12.The nuclear detector package of claim 11 wherein said interface includesa relatively large diameter threaded socket or hole.
 13. The nucleardetector package of claim 12 wherein said end adapter comprises a spacerhaving a surface that engages a matching surface on said interface ofsaid end cap.
 14. The nuclear detector package of claim 12 wherein athreaded stud or spindle is secured in said threaded socket or hole. 15.The nuclear detector package of claim 12 wherein an adapter containing aradiation calibration source is secured in said threaded socket or hole.16. The nuclear detector package of claim 10 wherein a positioningsleeve is located axially between said end cap and a rearward edge ofsaid support sleeve.
 17. The nuclear detector package of claim 1 whereinsaid nuclear detection element comprises a crystal wrapped withreflective tape.
 18. The nuclear detector package of claim 17 whereinsaid reflective tape is comprised of polytetrafluoroethylene.
 19. Thenuclear detector package of claim 17 wherein said shield is closed at anopposite end by a window engaging one end face of said crystal element.20. The nuclear detector package of claim 19 wherein said window isbrazed to one end of said shield.
 21. The nuclear detector package ofclaim 1 including spacer means for effectively increasing a lengthdimension of said end cap to thereby allow the nuclear detector packageto fit within tool housings otherwise too long for said nuclear detectorpackage.
 22. The nuclear detector package of claim 1 wherein nucleardetection is a scintillation detector.
 23. The nuclear detector packageof claim 1 wherein nuclear detection element is a neutron detector. 24.The nuclear detector package of claim 23 where the neutron detector is aHe3 proportional counter.